Method for agglomerating ore concentrate and resultant product

ABSTRACT

A method for agglomerating finely-divided starting material containing at least one chemically bound metal which is to be reduced out in a metallurgical process in which there is used a slag whose silicon content is higher than that of the slag forming components of the starting material, wherein the starting material is mixed with a finely-divided binder, consisting mainly of silica, and the mixture is formed into agglomerates which are maintained for from 1 to 48 hours in an atmosphere consisting mainly of steam at a temperature of 160* - 230*C and a pressure of 10 - 70 atmospheres above atmospheric.

[451 Apr.3,1973

[54] METHOD FOR AGGLOMERATING ORE CONCENTRATE AND RESULTANT PRODUCT [75]Inventor: Per Gudmar Kihlstedt, Bromma,

Sweden [73] Assignee: AB Cold Bound Pellets, Djursholm,

Sweden [22] Filed: Dec. 16, 1969 [21] Appl. No.: 885,614

[30] Foreign Application Priority Data Dec. 20, 1968 Sweden ..17614/68[52] U.S. Cl ..75/3, 106/120 [51] Int. Cl. ..C21b 1/24 [58] Field ofSearch ..75/3; 106/120 [56] References Cited UNITED STATES PATENTS765,789 7/1904 Peppel ..75/3 859,411 7/1907 Schumacher .....75/3 862,6668/1907 Schumacher... .....75/3 1,087,183 2/1914 Ronay ..75/3 1,520,89312/1924 Teitsworth 106/120 9/1957 Schumacher ..75/3

2,884,320 4/1959 Johnson ..75/3 3,235,371 2/1966 Volin et a1 ..75/33,257,220 6/1966 Kalousek et a1. ....106/120 3,386,816 6/1968Eng1ish..... ..75/3 X 3,505,439 4/1970 Moorehead et al.... ....106/120 X3,490,895 1/1970 Svensson ..75/3

FOREIGN PATENTS OR APPLICATIONS 1,154,614 5/1969 Great Britain ..75/3

Primary Examiner-Allen B, Curtis Attorney-Fleit, Gipple & Jacobson [57]ABSTRACT A method for agglomerating finely-divided starting materialcontaining at least one chemically bound metal which is to be reducedout in a metallurgical 7 Claims, No Drawings METHOD FOR AGGLOMERATINGORE CONCENTRATE AND RESULTANT PRODUCT The present invention relates to amethod for agglomerating finely-divided starting material containing atleast one chemically bound metal which is to be reduced out in ametallurgical process in which there is used a slag whose siliconcontent is higher than that of the slag forming components of thestarting material.

The normal procedure hitherto has been to form briquettes or pelletsfrom finely-divided ore concentrate and similar metal containingstarting materials and to sinter the briquettes or pellets by means of asuction sintering or pellet sintering process in which the agglomeratesare heated to approximately 1,400 and 1,250C, respectively. So-calledcold binding processes have also been suggested, in which agglomeratesare produced from the starting material, binding agent and water, and inwhich the agglomerates are treated with steam in a pressure autoclavewhich maintains a temperature of approximately 200C and a pressure ofapproximately atmospheres above atmospheric. In the cold bindingprocess, which is effected at a temperature'far below the sinteringtemperature of the substances present in the agglomerates, theagglomerates harden and so-called cold bound agglomerates are obtainedprovided that a suitable binding agent is used. Suitable binders areslaked lime, slalted steel furnace slag and cement, since these binders,either when used individually or in combination, are able to bindsatisfactorily magnetite or hematite type iron ore concentrates, forexample.

The normal binders, however, have been found unsuitable for use inproducing cold bound agglomerates in such instances where the valuablemetal in the agglomerates is to be reduced out in a metallurgicalprocess in which there is used a slag whose silicon content is higherthan that of the slag forming components of the starting material.Consequently, the cold bound agglomerates have made it necessary to addrelatively large quantities of materials riehin silica together with theagglomerates, which may render the process of recovering. the valuablemetals present in the agglomerates more difficult, and in all events iseconomically disadvantageous owing to the increased volume of slag. Whenconcerning the agglomeration of basic, and particularly ultra-basic oreconcentrates and similar starting material, it has been impossible 'toobtain satisfactory cold binding when using the normal binding agents.

The object of the present invention is to circumvent the above-mentioneddisadvantages and this is achieved by a method of the type defined inthe inmaterial may contain as a valuable component at least one of themetals Cu, Pb and Zn. Furthermore, the starting material may alsocontain a relatively high content of basic substances, for example basicgangue.

The binder used in the method of the invention and comprising mainlysilica should preferably be relatively finely-divided. The binder shouldsuitably present per gram a surface in excess of 3,000 cm. For example,the binder used may be finely-divided quartz which has been ground to aparticle size of 80 percent by weight below um. Even more finely groundmaterial can be used to advantage. Other finely-divided materials richin silica, such as silica-rich slag may be used instead of thefinely-divided quartz or in combination therewith. The binder may, tospecial advantage, consist at least partly of extremely finely-dividedmaterial comprising substantially silicon dioxide. Among such materialscan be mentioned so-called silicon fume, which, as is generally known,is obtained by a portion of the silicon reduced out during themetallurgical manufacture of silicon iron being vaporized. The vaporizedsilicon departs from the furnace and burns to the form of an extremelyfinely-divided dust comprised mainly of silicon dioxide. This material,which has a particle size below 1 pm and which ithas previously beenimpossible to use for any economical and useful purpose, can be used togreat advantage as a binder in the method of the present invention.Other silicarich dusts or powderous substances collected in airpurifying filters within the metallurgical industry and also within themolding and mining industry, can be used to advantage as a binder in themethod of the present invention. In certain instances the binder used inthe method may be permitted to contain more or less alkaline material,such as slaked steel furnace slag, Portland cement and slaked lime.Thus, in addition to material rich in silica, hydraulic material mayalso be used as a binding agent, in such quantities that theagglomerates are caused to contain up to 20 percent by weight binder.rich in silica and up to 10 percent by weight hydraulic binder. In otherwords, the binder can be composed of 67-100 percent silica and from O33percent of a hydraulic material. Or to put it still another way, thebinder may consist of up to one-third hydraulic material.

Normally the agglomerates are made to contain not more than 30 percentby weight binder, and usually they contain between 5 and 15 percent byweight binder. Thus, the agglomerates may contain about 70 v to percentiron ore fines.

troductory paragraph, wherein the starting material is mixed with afinely-divided or pulverulent binder, consisting essentially of silica,and the mixture is formed into agglomerates which are maintained forfrom 1 to 48 hours in an atmosphere consisting mainly of steam at atemperature of 230C and a pressure of 10 70 atmospheres aboveatmospheric.

The starting material may suitably consist of an ore concentrate or asecondary product, such as a product returned from a separating system,for instance a dust separating product obtained when treating oreconcentrate. For example, the ore concentrate may consist predominantlyof iron oxides or of chrome iron ore. In accordance with anotherembodiment, the starting The binder should be mixed intimately with thestarting material. The resulting mixture is suitably subjected to agrinding operation, in order to further homogenize the mixture, wherebymechanochemical reactions which promote the subsequent cold binding ofthe agglomerate constituents and which increase the strength of thefinal agglomerates can be caused to take place. The mixture is formed ina moist state into agglomerates, which can either be in the form ofbriquettes of desired shape or in the form of pellets produced byrolling methods. These agglomerates, which are as yet not cold bound,often contain more water than is suitable for the subsequent treatmentwith steam at elevated pressure and elevated temperature, and in suchcases the agglomerates may be pre-dried to the desired extend prior tosaid treatment. The agglomerates may be dried by passing the same alonga slowly moving bed, e.g. a conveyor belt, and flushing them with hotair and/or heating the same by a radiation heater.

In accordance with one exemplary embodiment of 5 the method of theinvention ultra basic chromite ore having the following composition wasagglomerated:

Cr O 54.0% by weight FeO 15.7% SiO 2.65% MgO 16.0% Al,0, l 1.2%

The binding agent used as so-called silicon fume ob tained from siliconiron manufacturing processes, containing approximately 90% Si0 in veryfinely-divided form. The chrome iron ore concentrate had a particle sizedistribution of approximately 80 percent by weight below 0.25 mm, and athird of this material was ground down to a particle size of 80 percentby weight below 0.10 mm, in order to facilitate pellet rolling andimprove the compacting degree. A mixture of 60 percent by weight of theoriginal chrome iron ore concentrate, 30 percent by weight according tothe above additionally ground concentrate and percent by weight siliconfume were ground and homogenized in wet state in a rod mill, whereafterthe ground material was rolled into pellet form on a pelletizing plate,a suitable quantity of water for rolling purposes being supplied duringthe process. Subsequent to the pellet rolling operation, the pelletswere flushed with hot air for 50 minutes as a preparatory measure priorto being treated in the autoclave and to impart to the pellets thenecessary degree of moisture. The pellets were treated in a steamautoclave for hours at 205C and a pressure of atmospheres aboveatmospheric. The obtained agglomerates presented excellent strengthproperties both in a cold state and during reduction in a hot state. Thecold pressure strength for pellets having a diameter of 12 mm was in theorder of 100 kp.

What is claimed is:

1. A process for agglomerating finely divided ferrous materialscontaining at least one chemically bound metal which is to be reducedout in a metallurgical process in which there is used a slag whosesilicon content is higher than that of the slag forming components ofthe finely divided ferrous materials comprising:

a. admixing said finely divided ferrous material with a binderconsisting essentially of 1. about 67 100 percent pulverulent silicahaving a specific surface area of at least 3,000 cm /gram and 2. about33 0 percent of a hydraulic material, the concentration of said binderin the composition being about 5 30 percent by weight,

b. forming the composition into agglomerates, and

c. heating said agglomerates for about 1 to 48 hours in a steamatmosphere at a temperature of about l60 to 230C at a pressure of about10 to atmospheres above atmospheric.

2. A method as claimed in claim 1 characterized in that the silicabinder is the silicon fume obtained from metallurgically manufacturingsilicon iron, said silicon fume further characterized in that itcontains extremely finely divided silicon dioxide.

3. A method as claimed in claim 1, characterized in that the bindingagent contains up to one-third hydraulic material.

4. A method as claimed in claim 1, characterized in that the particulateferrous material is chromium iron, iron ore or iron oxides.

5. A method as claimed in claim 1, characterized in that the particulateferrous material contains copper, lead or zinc.

6. A method according to claim 1 wherein the binder comprises 30 percentby weight of the mixture.

7. The product of the process of claim 1.

2. about 33 - 0 percent of a hydraulic material, the concentration ofsaid binder in the composition being about 5 - 30 percent by weight, b.forming the composition into agglomerates, and c. heating saidagglomerates for about 1 to 48 hours in a steam atmosphere at atemperature of about 160* to 230*C at a pressure of about 10 to 70atmospheres above atmospheric.
 2. A method as claimed in claim 1characterized in that the silica binder is the silicon fume obtainedfrom metallurgically manufacturing silicon iron, said silicon fumefurther characterized in that it contains extremely finely dividedsilicon dioxide.
 3. A method as claimed in claim 1, characterized inthat the binding agent contains up to one-third hydraulic material.
 4. Amethod as claimed in claim 1, characteriZed in that the particulateferrous material is chromium iron, iron ore or iron oxides.
 5. A methodas claimed in claim 1, characterized in that the particulate ferrousmaterial contains copper, lead or zinc.
 6. A method according to claim 1wherein the binder comprises 30 percent by weight of the mixture.
 7. Theproduct of the process of claim 1.